Modulator system



Filed May 15, 1950 Exciter Power Supply l AUdiO .73 Exciter H8 Oscillator Audio l 75 n9 Buffer -|3 2nd. Audio Isl. I5 Mulliplier Y I U IO 2nd. Multiplier 3!- u ID i Bl I ,lzl |2KV Moduloior Power Supply 30 Isl. Intermediate Power Amplifier 63 l 3 4 I27 IOKV a .6. :i PowerAmplifier fi Ploie Supply ZndJntermediote Power Am lifier p I 36 67 I 59 2] 37 T0 Antenna WITNESSES: INVENTORS Reuben Lee and lgolph N Harmon.

4h. 53 I 0W ATTORNEY and *to"-thelow voltage sideof" the reactor. "system is objectionable because the "modulation "transformer is likely to "be il'ar'ge and -costly.

frequency amplifier.

Patented June 10, 1952 UNITED STATES T 2,600,243 I IMODULATOR SYSTEM Ralph N. 'Harm'on, Baltimore, an'a' 'Beuljen Le'e, V Linthicum i Heights, Md., assigriers to westinghouse Electric Gorpo'rati'on, East"Pittsburgh, rPa.;a corporation of Pennsylvania AppIic'ation May'IE, 1950, Serial No."162;1 1 4 "6- Claims. (01. =332'"'43) 1 'Our invention -re-lates to electronic 'circuits 'and,more particularly,'to a system of high level modulation.

*One system conventionally iii'se'd for ampliacross a reactor, which is in turn connected "to the-plates of the--aniplifier tubes. A single anode 'power supply is connected 'to the midpoint of the modulation transformer primary winding This Moreover, its leakage reactanceandhistributed capacitance tend to cause frequency, phase, "and harmonic distortion at the high and '-low -ends of the -'a-udio'-"frequency range. =F'eedback used *to correct such distortion usually "cannot be derived from the secondary side of the modulation transformer, and so the beneficial-effects of such feedback are limited.

Another system f "the prior art or which we are 'aware utilizes an autotransformer which connects the modulator tubes through -a 'cou'pling capacitor across a reactor which 7 is in turn connected through a resistance 'anda radio-frequency choke to the anode circuit of *a radio- The midpoint of the autotransformer is connected to the low voltage side of the reactor and-also to a single '13. 'C. anode "potential supply which -is-' common to both the modulator and the "radio frequency amplifier. Such a system is incapable of -100%*modulation unless additional radio-frequency amplification stages are inserted. This latter system is exemplified 'by Patent No. --2;-226-,2l4 to H. D.

Albrecht.

-It is an obj ect of *ourinvention *to provide a system of modulation which avoids the objectionablefeaturesof prior art systems.

Another'obje'ct of 'our invention is to provide a system of highrlevel modulation wherein the advantages "of "feedback can be utilized and 100% modulation can be obtained.

Another object of our inventionis to provide a high lever :modulation capable of 100% modulation which does not employoa bulky and costly modulation transformer.

In accordance 'with "our invention, the anodes of the modulator tubes which'may be connected in push-pull relation "are joined through a center-tapped reactance which is coupled by a capacitor to the anode circuit of the radio-frequency amplifier. We provide two independent 'D. C. anode "power supplies, one of which is conneeted through a modulation reactor to "the ode potential to the modulator. The magnitude of the pot nua1=orthe modulator powersupply is m'aie-si-ifi'i'ciently greater than the potential of the radio-frequency amplifier power supply that modulation can be obtained.

' Other-objects and-advantages of our-invention will appear from the following 'de's'cription When-read in connection with theaccompanying 1 drawing in which thesingle figure is a schematic dia'gram showing -'a "preferred embodiment of our"invention.

The single 'fig'u're -'o'f the-"drawing "shows our invention as applied to the conventional radio transmitter. The various stages of the transmitter, which are conventional and do not constitute "the subject matter of our invention, are shown in the drawing as blocks in a line diagram. 'I-he Tadio frequency section comprises "stages which are -coupled in the following order: oscillator I {buffer 'l 3,-first multiplier 'I 5, second multiplier fH, first intermediate power amplifier 'ffl and second-intermediate "power amplifier 2!. The second intermediate power amplifier is coupled to the power amplifier, indicated g'enerally -at 23. The power amplifier includes 'two pairs of "paralleled amplifier tubes 25, 21 and 29, 31, -re's'pectively, connected in balanced push-pull relation. The grid and cathode circuits of [the *power amplifier are conventional and "are, therefore, shown as a block '33. The

, power amplifier output is taken through asymmetrical network Site the antenna input terfirst "capacitor 49, -aftu'n'a'b'le coupling "network 7 poweria'mpli'fiertubes 21, 3|. The coupling networlral comprises :a pair of variable capacitors '55, '51 connected'in series across a center-tapped coupling -"co il-3ii. The 'jiunctionof the variable capacitors 55, 5"1-"is "conne'cte'ol to" the "center 'tap 59 of the coupling coil 36 and to ground at 6|. The grids of power amplifier tubes 25, 29 are connected through a capacitor 38 and a radio frequency choke 40 to one terminal 42 of the tunable coupling network, and the grids of power amplifier tubes 21, 3] are connected through a capacitor 44 and a radio frequency choke 46 to the other terminal 48 of the tunable coupling network 5|. The antenna coupling coil 50 is connected across the antenna input terminals 31, and in inductive relation to the coupling coil 35 of the tunable network 5|. A lkv. power amplifier plate supply 53, shown as a block, is connected from its high potential side through a filter choke 65 and a modulation reactor 61 to the junction of the radio frequency chokes 39, 41. The junction of the filter choke 65 and the modulation reactor 61 is connected through a capacitor 69 to ground II.

The audio section of the transmitter includes audio input I3 and first, second, third, and fourth audio amplifiers I5, TI, 19, 8I coupled in that order. The fourth audio amplifier BI is coupled to the modulator stage which is indicated generally at 83. The modulator stage includes two pairs of paralleled audio amplifier tubes 85, 81, and 89, 9!, respectively connected in balanced push-pull relation. The conventional grid and cathode circuits of the modulator are shown as a block 93. The anode output terminals of the modulator 83 are connected through resistance 99, IN, capacitance I03, I05, resistance I01, I09 and capacitance III, I I3, respectively, to ground H5. Feedback is taken from the junctions of the resistance I 01, I09 and capacitance I03, I05, respectively, via conductors H8, H9 to the first audio amplifier I5. The output terminals 95, 91 of the modulator tube anode H! are bridged by a center-tapped reactor H9. The high voltage terminal of a 12 kv. modulator power supply I2 I, shown as a block, is connected through a filter choke I23 to the center tap I25 of the centertapped reactor I I9 and through a by-pass capacitor I28 to ground I29. The modulator B3 is coupled to the power amplifier 23 by means of a coupling capacitor I21 which is connected from one output terminal I30 of the modulator to a point common to the modulation reactor .61 and the second and third chokes 49, which are connected in the power amplifier output circuit 35.

The use of a center-tapped reactor instead of a modulation transformer in the output circuit of the modulator makes-it possible to fully utilize the beneficial effects of feedback. The employment of separate and independent D. C. power amplifier and modulator plate supplies makes it possible to conveniently and efficiently obtain 100% modulation, with a minimum of radio frequency amplifier stages. 7

We are aware that certain modifications of our invention, without departure from the scope thereof, will appear to those skilled in the art. We desire, therefore, that our invention be given an interpretation as broad as isconsistent with the prior art and the spirit of the appended claims.

We claim as our invention:

1. A system of modulation including a modulator having a double-ended output, a centertapped reactor connected in balanced relation to the output of said modulator, a conductor adapted to connect the center tap of said reactor to a first anode voltage supply, a radio-frequency amplifier, means for coupling said modulator to said radio-frequency amplifier, and'a modulation renected in series with said anodes, a conductor adapted to connect the center'tap of said reactor to a first source of anode potential, a reactor, a coupling capacitor, a first terminal adapted for connection to a second anode potential source, a conductor connecting said first terminal to one side of said reactor, conductors connecting the other side of said reactor and one side of said coupling capacitor to said second terminal, and a conductor connecting the other side of said coupling capacitor to a point common to said center-tapped reactor and one of said anodes.

3. A system of high level modulation including an audio-frequency amplifier having a double-ended output, said amplifiers including electric discharge devices each having an anode, a cathode, and a control element, a radio-frequency amplifier having a double-ended output, means for coupling the outputs of said amplifiers in single-ended relation, said means including a first reactor connected in balanced relation to the output of said audio-frequency amplifier, a sec ond reactor connected in the anode power supply circuit of said radio-frequency amplifier, a capacitor coupling said reactors, and a connection from the midpoint of said first reactor in the anode power supply circuit of said audio-frequency amplifier, the anode power supplies of said amplifiers being independent of each other.

4. The invention according to claim 3, wherein the Potential of the audio-frequency amplifier anode power supply is sufiiciently higher than the potential of the radio-frequency amplifier anode power supply that modulation can be obtained.

5. A pair of electric discharge devices having their anodes joined through a first reactor, a capacitor connected to one of said anodes and through a second reactor to a first source of direct current anode potential, a second source of direct current anode potential connected to the midpoint of said first reactor, and capacitors connected to by-pass said potential sources to ground.

6. A pair of electric discharge devices having their anodes joined through a first reactor, a capacitor connected to one of said anodes and through a second reactor to a first source of direct current anode potential, a second source of direct current anode potential independent of and of greater magnitude than said first potential source connected to the midpoint of said first reactor, and capacitors connected to by-pass said potential sources to ground.

RALPH N. HARMON. REUBEN LEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Edwards Sept. 5, -0 

